The unit expressing the minimum indoor combustion air is ft³/1000 BTU/hr. Which option is correct?

The unit expressing the minimum indoor combustion air is ft³/1000 BTU/hr. Which option is correct?

• A. ft³/BTU
• B. ft³/100 BTU/hr
• C. ft³/1000 BTU/hr
• D. m³/1000 BTU/hr

Answer: (C)

The amount of indoor combustion air is tied to how much heat the appliance can produce, so the requirement is given as air volume per unit of heat input. Using cubic feet of air per 1000 BTU per hour standardizes the rule: for every 1000 BTU/hr the appliance can input, a specific amount of air is needed. This makes it easy to scale the ventilation for any appliance by its BTU/hr rating and keeps the measurement consistent with code language. That’s why the correct unit is ft³/1000 BTU/hr. The other options don’t fit the common practice: ft³/BTU or ft³/BTU/hr mix volume with energy without the hourly basis, ft³/100 BTU/hr would use an incorrect base for scaling, and using metric volume (m³) isn’t standard in this context.

The amount of indoor combustion air is tied to how much heat the appliance can produce, so the requirement is given as air volume per unit of heat input. Using cubic feet of air per 1000 BTU per hour standardizes the rule: for every 1000 BTU/hr the appliance can input, a specific amount of air is needed. This makes it easy to scale the ventilation for any appliance by its BTU/hr rating and keeps the measurement consistent with code language.

That’s why the correct unit is ft³/1000 BTU/hr. The other options don’t fit the common practice: ft³/BTU or ft³/BTU/hr mix volume with energy without the hourly basis, ft³/100 BTU/hr would use an incorrect base for scaling, and using metric volume (m³) isn’t standard in this context.